PARIS, FRANCE—Periods of wet weather in South Africa led to population growth and cultural advancement in modern humans during the Middle Stone Age, according to a comparison of the archaeological record and climate history read from a sediment core. The use of symbols, the development of complex language, the manufacture and use of stone tools, and the creation of jewelry all coincided with climate change, according to Martin Ziegler of the Cardiff University School of Earth and Ocean Sciences. “At the same time, large parts of sub-Saharan Africa experienced drier conditions, so that South Africa potentially acted as a refuge for early humans,” he added.